On my Dad's side, My grandfather, then my Dad, kept us fully informed once they felt we were mature enough to understand how things worked. Probably around 25 or so.

We started having annual family meetings with our kids when they were 25 or so where we'd give them a copy of our financial statement. They've also attended meetings with attorneys regarding our Wills the last couple of times we've had such meetings.

My Mom's family was very secretive which, I believe, made it harder for us to help them when they became infirm.

But, in the end, it depends on your kids. Are they responsible or are they jackasses? Or somewhere in the middle? Depending on where they fall on this continuum would inform my decision.